1. Field of the Invention
The present invention relates to cable rotary joints, and particularly to an arrangement in which a length of wire or fiber-optic cable is transferred between a pair of spools to effect a number of rotations between opposite ends of the cable.
2. Discussion of the Known Art
Certain telemetry and data link systems must ensure continuity of signals across a rotating interface. A rotating interface is presented, for example, by a stationary receiver on the deck of a ship, and an instrumentation unit that is towed at the end of an electrical or fiber optic cable. The instrument side of the cable is reeled up and down by a winched cable storage drum on the ship's deck. The receiver side of the cable exits from a hub region of the drum, and therefore rotates or twists in unison with rotation of the drum.
Thus, in order for the instrumentation unit to maintain a continuous and unbroken connection with the receiver via the cable while the cable drum rotates many revolutions in either sense of rotation, an interface tolerant of cable rotation must be provided between the rotating end of the cable exiting from the drum, and the stationary receiver on the ship's deck. One such interface is disclosed in U.S. Pat. No. 3,822,834 (Jul. 9, 1974). The device of the '834 patent is designed to transfer electrical and hydraulic cables, pneumatic hoses, and other sturdy lines capable of being level-wound in many layers without damage by large scale reels.
With the recent application of optical fiber to cabled telemetry systems, optical "rotors" have been developed which provide acceptable optical continuity of a limited number of fibers across rotating joints of unlimited revolutions, in either sense of rotation. Most known fiber optic rotors rely on various techniques of optically jumping a gap between a stationary and a rotating side of the joint, the most straightforward involving optically jumping a gap between two opposing lensed fiber ends which are precisely aligned on the axis of rotation.
U.S. Pat. Nos. 5,078,466 (Jun. 7, 1992) and 5,450,509 (Sep. 12, 1995) disclose optical rotary joints that spool a stiffened ribboned fiber matrix off of the outside of an inner cylindrical surface, and onto the inside of a coaxial outer cylindrical surface. Both of the patented devices require a large ribboned fiber that is adhered to a stiffening material to maintain winding control. Both devices are thus limited in the number of cable rotations available per a given housing volume.